Motor vehicle components are often produced by means of hot-forming a cold-rolled or hot-rolled steel sheet. Examples of such automotive steel products are vehicle columns, supports, bumpers, rocker panels, fuel tank assemblies, door frames, and components such as parts of the floor of the motor vehicle. Hot-forming is carried out at a temperature greater than 700° C. and often includes a step of hot-stamping the steel sheet. Hot-forming increases the mechanical strength and improves other physical properties of the steel sheet.
The high temperatures that are used during hot-forming lead to the formation of oxide layers on the steel sheets, which can result in scale and corrosion, or decarbonization of the surface of the steel sheets, and thereby reduce the mechanical strength of the steel sheets and cause increased wear on the forming tools during hot-forming. These surface effects also lead to poor adhesion characteristics, making it difficult to paint the surface of the resulting component. Subjecting the hot molded steel part to shot-blasting removes the surface defects, also but requires a high degree of energy and may negatively affect other properties of the component.
A coating for a steel component is known from WO2013166429, which coating uses a non-metallic layer of at least silicon and carbon, in order to improve the surface effects before and during the hot-forming process and, if applicable, to prevent them from arising in the first place. The non-metallic coating has a plurality of individual layers, preferably one to three different layers. The layers together have a total thickness of not more than 300 nm, and preferably not more than 100 nm.
It would desirable to simplify the layer system for series production, and to minimize the layer structure in the respective layer thickness, without losing the desired properties.